Question

In Java is there something similar to C++ Standard Library lists that uses a comparator to find a specific object in a list by one of its variables?

For instance instead of looping through an ArrayList looking for a specific Object by checking for the variable comparison. Is there a way to use a comparator object to find a specific instance?

(Note: I don’t want to use a hashmap as that would create two seperate lists. I want the functionality of a list without having to have a hashmap involved.)

Something like this, but for Java:

#include <algorithm>

using namespace std;

class Cperson     
{    
  string lastname, firstname, address, city;    
  int zipcode;    
  char state[3];    
  // this works for the last name    
  friend bool operator==(const Cperson& left, const Cperson& right);    
  friend bool firstEqualTo(const Cperson& left, const Cperson& right);    
};

bool operator==(const Cperson& left, const Cperson& right)    
{    
  return left.lastname == right.lastname;    
}

bool firstEqualTo(const Cperson& left, const Cperson& right)    
{    
  return left.firstname == right.firstname;    
}     

Now we can search our personlist on the firstname field, ignoring the other fields:

vector<Cperson> personlist;    
// fill personlist somehow

Cperson searchFor;   // should contain the firstname we want to find    
vector<Cperson>::iterator fperson;   
fperson= std::find(personlist.begin(),    
                   personlist.end(),   
                   searchFor,    
                   firstEqualTo);

Answer 1

If you can use Google Guava have a look at that question and its answers: Filtering on List based on one property with guava

Update:

If you don’t like Google and thus don’t want to use their libraries, try Apache Commons Collections’ CollectionUtils:

List<Person> filteredList = new ArrayList<Person>(allPersons);
CollectionUtils.filter( filteredList, new Predicate() {
  boolean evaluate(Object object) {
    //do whatever you want
  }
});

The downside is that Commons Collections itself doesn’t use Generics. There is a generic port of Commons Collections 3.1, however.